Field of the Invention
The present invention relates to a method for manufacturing a glass cliché using laser etching and an apparatus for laser irradiation therefor, and more particularly to a method for manufacturing a glass cliché using the phenomenon that an etching speed of glass is relatively increased only in a portion to which laser is irradiated.
Description of the Related Art
To produce a flat panel display (FPD) such as a liquid crystal display (LCD) and a plasma display panel (PDP), various kinds of patterning processes for making electrodes, black matrix, color filters, separators, thin film transistors and so on are required.
In a general case, a photoresist is selectively removed using a photo mask by exposing and developing to make a photoresist pattern, and then the photoresist pattern is used for the patterning process. This patterning process using a photo mask uses a lot of materials such as photoresist and developing agent and also needs an expensive photo mask, which results in many processing steps or long processing time.
To solve this problem, there have been proposed various methods for printing a pattern-forming material directly such as ink jet printing or laser transcription, without using photoresist. As one of such methods, there is an offset printing in which a patterned material is transcribed to a blanket using a cliché and then the pattern of the blanket is transcribed onto a cliché.
The offset printing using a cliché ensures smaller material consumption and simpler process than a conventional method using photoresist and also ensures faster process speed than ink-jet printing or laser transcription. However, the offset printing needs clichés independently for substrates with different patterns, and a cliché generally made of glass is manufactured complicatedly and very expensive.
A general method for making the glass cliché is explained with reference to FIG. 1. A photoresist 102 is applied onto a glass cliché 101 by means of spin coating, dip coating, spray coating, slit coating, bar coating or the like, as shown in FIG. 1(a).
After that, a photo mask 103 is used to form a desired pattern as shown in FIG. 1(b) by means of exposure and development phenomena. During the exposure process, the photoresist 102 is selectively photo-sensitized by UV rays 104 passing through the photo mask 103 in which a desired pattern is already formed, and a pattern 105 is formed on the glass cliché as shown in FIG. 1(c) due to the difference of solubility for a developing solution between the photo-sensitized region and the non-sensitized region.
FIG. 1(c) shows the case adopting a positive photoresist, but a negative photoresist may also be used. In case the negative photoresist is used, a region irradiated by UV rays 104 remains but a region not photo-sensitized by UV rays is removed.
The glass cliché having the pattern of the photoresist 102 formed therein is dipped in a glass etching solution (not shown) as shown in FIG. 1(d), and then glass etching reaction occurs partially only on a region 106 where a glass cliché is exposed. Generally, an etching reaction of an amorphous material such as glass becomes an isotropic etching without no orientation, so an etching speed is identical in both depth and width directions of the glass.
Thus, as the etching reaction occurs, a glass etching region 106 becomes wider than the width of the pattern of the photoresist 102, and a bottom portion of the etching portion has a rounded shape, as shown in FIG. 1(d). As the etching work progresses, the etching continuously occurs in depth and width directions as shown in FIG. 1(e), so a width 107 of the etched glass cliché becomes gradually wider than the pattern of the photoresist 102.
If the etching is completed to a desired depth, the glass cliché is taken out of the etching solution and washed by a distilled water, and then the photoresist is removed to obtain a glass cliché 108 finally etched, as shown in FIG. 1(f).
In the method of making a glass cliché using such a wet etching, isotropic etching occurs as shown in FIG. 1, so the pattern is etched in its sides as much as the same thickness as the etched depth.
Thus, the pattern of photoresist used for etching should be formed with at least double margin of a desired etching depth, and due to this reason, there is a limit in precision for the pattern to be formed. Also, considering a room where an etching solution may penetrate, an actually etchable pattern should be three or four times as much as a minimal etching depth, so it is more difficult to form a pattern with fine line widths.
In addition, due to the nature of isotropic etching, the etching is made in a substantially circular shape between a wall and a bottom to be etched, so an etching depth is gradually varying, which results in deteriorated printing quality. Also, since a photoresist pattern should be formed prior to the etching process, many processes such as an exposure process using a photo mask and a photoresist development process using a developing solution are needed before the etching work, and also a process of removing the remaining photoresist is also added after the etching work is completed.
In addition to the above wet etching, a dry etching for etching a glass using plasma of an etching gas in a vacuum state is also available. The dry etching for etching a glass cliché using a gas containing fluorine such as CF4 and CF3H allows anisotropic etching, differently from the wet etching, so a line width is not widened or a region between a wall and a bottom is not etched in a circular shape as the dry etching progresses.
However, a vacuum chamber and an expensive etching gas should be prepared for the dry etching, which increase a cost for the etching work and makes it difficult to apply the etching work to large-scale matters or mass production.
Also, the drying etching makes an etching mask and an etching material be etched together, so the etching mask should have as slowest etching speed as possible. Generally, a mask layer made of metal such as chrome is used for glass etching, but this mask layer cannot be made too thick, so there is a limit in glass etching depth.
In addition, the dry etching needs to form a mask pattern prior to etching, similarly to the wet etching, so many processes such as preprocesses for vacuum-deposition of a metal mask layer, formation of a photoresist layer, exposure of the photoresist using a photo mask, development of the photoresist layer to form a pattern, etching of the metal layer used as a mask as well as postprocesses for removal of the metal mask after etching are required.
In order to solve the above problems in a glass cliche making process using wet etching or dry etching, a new method using laser etching is proposed in the Korean Laid-open Patent Publication No. 10-2007-0000100 or the like.
The Korean Laid-open Patent Publication No. 10-2007-0000100 discloses a method for making a cliché having a desired pattern by directly etching an insulating substrate with laser. In case a glass cliché is directly etched with laser to make a cliché, there may be advantages in process since an etching solution is not used. However, since the glass is removed by means of photothermolysis on regions irradiated by laser, the used laser should have a high power and an etching speed is relatively slow. Also, it is impossible to prevent generation of HAZ (Heat Affected Zone) that may cause pattern deterioration, and fine cracks may happen in the glass cliché due to thermal impacts caused by continuous irradiation of the laser with strong energy.
Along with them, since a roll means playing a role of moving a material transcribed to a glass cliché continuously transfers load to the glass cliché, the load may weaken durability of the glass cliché or causes fine cracks in the glass cliché. Also, residuals of pattern material, not moved by the roll means, may remain in a blanket.